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3 years ago

How do you know how many valence electrons are in a molecule?

Chemistry

2 answers:

telo118 [61]3 years ago

4 0

1. by making a atomic configuration
2.by making a table of shells of k.l.m.n....
that's all

Leno4ka [110]3 years ago

4 0

To know the number of valence electrons you must know the number of electrons in the outer shell .. In the periodic table there are 8 groups (which are the vertical columns) .. ignore the yellow ones for now which are the transition metals .. the group number is the number of electrons in the most outer shell of an atom .. so for example lithium and sodium are in group 1 so they have only 1 electron in their outer shell .. the valence electrons are the ones an atom looses or gains during a chemical reaction (atoms try to be stable by having 8 electrons in their outer most shell) .. for example atoms in group 1 have 1 electron in their outer shell that they want to loose so the valency is 1 .. In group 5 they need to become 8 so they gain 3 electrons so the valency is 3

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9. Write a balanced nuclear equation for the following: The isotope Strontium-90 decays by Q-

Sergio039 [100]

Answer: $_{38}^{90}\textrm{Sr}\rightarrow _{36}^{86}\textrm{Kr}+_2^4\textrm{He}$

Explanation:

Alpha Decay: In this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. The mass number is reduced by 4 units and atomic number is reduced by 2 units.

General representation of an element is given as: $_Z^A\textrm{X}$

where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

General representation of alpha decay :

$_Z^A\textrm{Sr}\rightarrow _{Z-2}^{A-4}Y+_2^4\alpha$

The balanced nuclear equation when the isotope Strontium-90 decays by Q- decay is :

$_{38}^{90}\textrm{Sr}\rightarrow _{36}^{86}\textrm{Kr}+_2^4\textrm{He}$

4 0

3 years ago

A substance registers a temperature change from 20 to 40 to what incremental temperature change does this correspond

ss7ja [257]

Given:

Initial temperature, T1 = 20 C

Final temperature, T2 = 40 C

To determine:

The temperature change

Explanation:

Convert degree C to Kelvin

Temperature in Kelvin = degree C + 273

T1 = 20 + 273 = 293 K

T2 = 40 + 273 = 313 K

Incremental temperature change = T2 - T1 = 313-293 = 20 K

Ans: The temperature change in kelvin is 20 K

3 0

3 years ago

If 8.50 g of phosphorus reacts with hydrogen gas at 2.00 atm in a 10.0-L container at 298 K, calculate the moles of PH3 produced

ahrayia [7]

Answer:

The moles of PH₃ produced are 0.2742 and the total number of moles of gas present at the end of the reaction is 0.6809.

Explanation:

Phosphorus reacts with H₂ according to the balanced equation:

P₄ (s) + 6 H₂ (g) ⇒ 4 PH₃ (g)

By stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of each compound participate in the reaction:

P₄: 1 mole
H₂: 6 moles
PH₃:4 moles

Being the molar mass of the compounds:

P₄: 124 g/mole
H₂: 2 g/mole
PH₃: 34 g/mole

The following mass amounts of each compound participate in the reaction:

P₄: 1 mole* 124 g/mole= 124 g
H₂: 6 mole* 2 g/mole= 12 g
PH₃: 4 moles* 34 g/mole= 136 g

An ideal gas is characterized by three state variables: absolute pressure (P), volume (V), and absolute temperature (T). The relationship between them constitutes the ideal gas law, an equation that relates the three variables if the amount of substance, number of moles n, remains constant and where R is the molar constant of the gases:

P * V = n * R * T

In this case you know:

P= 2 atm
V= 10 L
n= ?
R= 0.082 $\frac{atm*L}{mol*K}$
T= 298 K

Replacing:

2 atm*10 L= n*0.082 $\frac{atm*L}{mol*K}$ *298 K

and solving you get:

$n=\frac{2 atm*10 L}{0.082\frac{atm*L}{mol*K}*298 K }$

n=0.818 moles

The limiting reagent is one that is consumed first in its entirety, determining the amount of product in the reaction. When the limiting reagent is finished, the chemical reaction will stop.

To determine the limiting reagent, you can use a simple rule of three as follows: if 6 moles of H₂ react with 124 g of P₄, 0.818 moles of H₂ with how much mass of P₄ will it react?

$mass of P_{4}=\frac{0.818 moles of H_{2}*124 grams of P_{4}}{6 moles of H_{2}}$

mass of P₄= 16.90 grams

But 16.90 grams of P₄ are not available, 8.50 grams are available. Since you have less mass than you need to react with 0.818 moles of H₂, phosphorus P₄ will be the limiting reagent.

Then you can apply the following rules of three:

If 124 grams of P₄ produce 4 moles of PH₃, 8.50 grams of P₄, how many moles do they produce?

$moles of PH_{3} =\frac{8.5 grams of P_{4}*4 moles of PH_{3} }{124grams of P_{4}}$

moles of PH₃=0.2742

If 124 grams of P₄ react with 6 moles of H₂, 8.50 grams of P₄ with how many moles of H₂ do they react?

$moles of H_{2} =\frac{8.5 grams of P_{4}*6 moles of H_{2} }{124grams of P_{4}}$

moles of H₂= 0.4113

If you have 0.818 moles of H₂, the number of moles of gas H₂ present at the end of the reaction is calculated as:

0.818 - 0.4113= 0.4067

Then the total number of moles of gas present at the end of the reaction will be the sum of the moles of PH₃ gas and H₂ gas that did not react:

0.2742 + 0.4067= 0.6809

Finally, the moles of PH₃ produced are 0.2742 and the total number of moles of gas present at the end of the reaction is 0.6809.

5 0

3 years ago

202H8(9) + 7 O2(g) > 4CO2(g) + 6 H2O(9).

lilavasa [31]

since the concentration of Carbon Dioxide will increase, it would make Q > K, cause equilibrium to shift in the direction with less moles of gas to alleviate the extra pressure. In this case, the reaction will shift left because there are fewer moles of gas present.

4 0

2 years ago

What is Delta.Gsystem for the system that is described by the following data? Delta.Hsystem = –345 kJ, T = 293 K, Delta.Ssystem

ryzh [129]

Answer:

-209 kJ

Explanation:

I did the math. You're welcome ;)

6 0

3 years ago